This invention relates to an apparatus employing a cylinder combustion pressure sensor to monitor cylinder combustion in an internal combustion engine.
In order to achieve high engine performance and high fuel economy, it is desired to control the engine in a manner to establish optimum cylinder combustion. For this purpose, it is the current practice to monitor cylinder combustion by employing a cylinder combustion pressure sensor which is secured to the engine by a spark plug or cylinder head bolt tightened to rated torque so as to produce a sensor signal indicative of a sensed cylinder combustion pressure level to a control circuit. In the event of engine misfire or failure of the cylinder pressure sensor and the associated signal line, however, the sensor signal become unreliable, causing the control circuit to control the engine toward undesirable cylinder combustion resulting in poor engine performance.